American Express customers first need to sync their credit cards to their Twitter accounts. They can then tweet specific hashtags to buy American Express gift cards and products from Amazon, Urban Zen, and Xbox 360. AmericanExpress will reply via Twitter with a confirmation hashtag, and ask the user to confirm the purchase in a tweet.

Twitter, which has mostly relied on advertising for revenue, could now potentially have a new source of revenue. But neither Twitter nor American Express are willing to discuss the financial terms of the partnership, Shira Ovide of The Wall Street Journal reports.

“We’re convinced that commerce is going to be one of the areas (for which) advertisers are going to start using our platform,” Twitter's VP of Global Brand Strategy Joel Lunenfeld, told WSJ.

American Express already has similar card-sync deals in place with Facebook, Foursquare, and Xnox Live, but they're merely to offer discounts. This is the first time American Express is actually allowing people to make purchases through a social network.